Light-emitting element and iridium complex

ABSTRACT

A light-emitting element having excellent light-emitting properties and with which it is possible to emit blue light at a high luminance for a long period of time, and an iridium complex for realizing the same. The light-emitting element has an external quantum efficiency of at least 5% and a light emission maximum wavelength λmax of no more than 500 nm. Further, there is provided a light-emitting element including a light-emitting layer or a plurality of organic compound layers having the light-emitting layer, with at least one of the compound layers including at least one kind of a compound having a partial structure represented by the general formula K-0. In the general formula K-0, R 1  to R 7  each independently represents a hydrogen atom or a substituent, provided that if R 2  is a fluorine atom, R 3  is not a hydrogen atom

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel iridium complex and alight-emitting element that uses the novel iridium complex. Moreparticularly, the present invention relates to a novel iridium complexand a light-emitting element that uses the novel iridium complex thatcan be appropriately used in display elements, displays, backlights,electrophotography, illumination light sources, recording light sources,exposure light sources, read light sources, signs, signboards, interioroptical communication and the like.

2. Description of the Related Art

At present, research and development relating to various kinds ofdisplay elements are actively being carried out. In particular, organicelectroluminescent (EL) elements have received attention as promisingdisplay elements because EL elements can emit highly luminous light at alow voltage. For example, a light-emitting element having an organicthin film formed by vapor deposition of an organic compound has beenknown (Applied Physics Letters, Vol. 51, p. 913 (1987)). Light-emittingelements disclosed in the literature use tris(8-hydroxyquinolinate)aluminum complex (Alq) as an electron transporting material, and have astructure comprising a layer containing the electron transportingmaterial and a layer containing a hole transporting material (an aminecompound) laminated together. In comparison to conventionallight-emitting elements comprising a single layer, light-emittingcharacteristics can be greatly improved with light-emitting elementscomprising laminated layers. In recent years, the application of organicEL elements to color displays and white light sources has been activelyinvestigated. In order to apply organic EL elements to such ends, it isnecessary to improve the light-emitting properties of the organic ELelements, such as luminance and light-emitting lifespan, with regard tolight-emitting elements that are capable of emitting light in blue,green and red colors, respectively.

As a light-emitting element having improved light-emitting properties, alight-emitting element utilizing light emission from an orthometalatediridium complex (Ir(ppy)₃: tris-orthometalated complex of iridium (III)with 2-phenylpyridine) has been reported (Applied Physics Letters, Vol.75, p. 4 (1999)). While it has conventionally been said that theexternal quantum efficiency of light-emitting elements is limited to 5%,light-emitting elements disclosed in the literature reach an externalquantum efficiency of 8%, which exceeds the conventional limitation.However, the emitted light obtained from the light-emitting element islimited to green light emission, and the applicable range as a displayis narrow. The applicable range as a display could be expanded iflight-emitting elements having improved light-emitting characteristicsfor other colors could be provided. Thus, there has been a demand toimprove light-emitting characteristics of light-emitting elements ofother colors.

With respect to blue light-emitting elements, various light-emittingelements have been reported that use a distyrylallylene derivative,represented by DPVBi (4,4′-bis(2,2′-diphenylvinyl)biphenyl), and ananalog thereof. However, there have been no reports of bluelight-emitting elements having an external quantum efficiency exceeding5%. If a blue light-emitting element having an external quantumefficiency exceeding 5% could be provided, it would be possible for ahighly efficient organic EL element to display multicolors and whitecolor, whereby application of light-emitting elements would be greatlyadvanced. Moreover, it would be possible to greatly reduce electricalpower consumption and to realize large area display and long term usewhen the light-emitting element is applied to a display element.

SUMMARY OF THE INVENTION

The present invention has been developed in view of the foregoingproblems. An object of the invention is to provide a light-emittingelement that can reduce energy consumption when light is emitted, thathas excellent light-emitting properties, and with which it is possibleto emit blue light at a high luminance for a long period of time.

Another object of the invention is to provide an iridium complex havingexcellent light-emitting properties and with which it is possible toemit blue light at a high luminance for a long period of time, and alight-emitting element that uses the iridium complex.

As means to accomplish these objects, the present invention provides thefollowing light-emitting elements and iridium complexes:

-   (1) a light-emitting element having an external quantum efficiency    of at least 5% and a light emission maximum wavelength λmax of no    more than 500 nm;-   (2) a light-emitting element containing a light-emitting material,    with a phosphorescence quantum yield of the light-emitting material    being at least 70% at 20° C. and a phosphorescence emission maximum    wavelength λmax of the light-emitting material being no more than    500 nm;-   (3) a light-emitting element comprising a light-emitting layer or a    plurality of organic compound layers including the light-emitting    layer disposed between a pair of electrodes, wherein at least one of    the compound layers includes at least one kind of a compound having    a partial structure represented by the following general formula    K-0:

wherein R¹ to R⁷ each independently represents a hydrogen atom or asubstituent, provided that if R² is a fluorine atom, R³ is not ahydrogen atom;

-   (4) an iridium complex represented by the following general formula    K-II:

wherein R²¹ to R²⁶ each independently represents a hydrogen atom or asubstituent; L²¹ represents a ligand; n²¹ represents an integer of 1 to3; and n²² represents an integer of 0 to 4;

-   (5) an iridium complex represented by the following general formula    K-IV:

wherein R⁴¹ to R⁴⁶ each independently represents a hydrogen atom or asubstituent; L⁴¹ represents a ligand; n⁴¹ represents an integer of 1 to3; and n⁴² represents an integer of 0 to 4;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The light-emitting element of the present invention is characterized inthat it exhibits blue light emission at a light emission maximumwavelength λmax of 500 nm or less and a high light emission efficiencywith an external quantum efficiency of 5% or more. Therefore, thelight-emitting element of the present invention can reduce energyconsumption at the time light is emitted and can emit highly luminousblue light for a long period of time. Particularly, when thelight-emitting element of the present invention is used as a displayelement, it becomes possible to increase surface area. The externalquantum efficiency referred to herein means the value calculated by theequation below. Examples of methods of calculating the external quantumefficiency of the light-emitting element include a method in whichexternal quantum efficiency is calculated from luminance of emittedlight, light emission spectrum, relative visibility curve and electriccurrent density, and a method in which external quantum efficiency iscalculated from electric current density and total number of emittedphotons.external quantum efficiency (%)=(total number of emitted photons/numberof electrons injected in light-emitting element)×100

The external quantum efficiency of the light-emitting element ispreferably 7% or more, and more preferably 10% or more. Thelight-emitting element of the present invention preferably has a lightemission maximum wavelength λmax of from 390 to 495 nm, more preferablyfrom 400 to 490 nm, and further preferably from 420 to 480 nm, from thestandpoint of color purity of blue color.

The light-emitting element of the present invention may, as long as ithas a light emission maximum wavelength of 500 nm or less, exhibit lightemission in a wavelength region other than the blue region, such as anultraviolet region, a green region and a red region.

It is preferable that an x value and a y value of the CIE chromaticityof light emission are as small as possible from the standpoint of thecolor purity of blue color. Specifically, the x value of the CIEchromaticity of light emission is preferably 0.22 or less, and morepreferably 0.20 or less. The y value of the CIE chromaticity of lightemission is preferably 0.53 or less, more preferably 0.50 or less, andfurther preferably 0.40 or less.

The light-emitting element preferably has a light emission spectrum halfvalue width of 1 to 100 nm or less, more preferably from 5 to 90 nm,further preferably from 10 to 80 nm, and particularly preferably from 20to 70 nm, from the standpoint of the color purity of blue color.

The light-emitting element is not particularly limited with respect tosystem, driving method and utility mode, and examples thereof include EL(electroluminescent) elements. One example of such an EL elementincludes a light-emitting element in which at least one light-emittinglayer is formed between a pair of electrodes comprising an anode and acathode. Other examples include a light-emitting element in which atleast one of a hole implantation layer, a hole transporting layer, anelectron implantation layer and an electron transporting layer isfurther disposed between the electrodes, in addition to thelight-emitting layer. These layers may each have other functions, andvarious materials can be used to form each of the layers. Thelight-emitting element of the present invention is preferably an organiclight-emitting element. The organic light-emitting element referred toherein means an element in which a material which exhibits emission oflight is an organic compound.

In the light-emitting element, it is preferable that a layer containinga compound having an ionization potential of 5.9 eV or more, morepreferably from 6.0 to 7.0 eV, is disposed between the cathode and thelight-emitting layer, and it is more preferable that an electrontransporting layer having an ionization potential of 5.9 eV or more isdisposed between the cathode and the light-emitting layer.

In the light-emitting element, a material having a high phosphorescencequantum yield is preferably used as the light-emitting material.Specifically, a light-emitting material having a phosphorescence quantumyield of 70% or more at 20° C. and a phosphorescence emission maximumwavelength λmax of 500 nm or less is preferable. A light-emittingmaterial having a phosphorescence quantum yield of 80% or more at 20° C.and a phosphorescence emission maximum wavelength λmax of 490 nm or lessis more preferable. A light-emitting material having a phosphorescencequantum yield of 85% or more at 20° C. and a phosphorescence emissionmaximum wavelength λmax of 480 nm or less is still further preferable.

The above-described light-emitting material is a compound contained in alight emitting layer of the light emitting element, or in organiccompound layers including the light emitting layer, which compounditself emits light. A transition metal complex is preferable as thelight-emitting material, and an orthometalated complex is morepreferable. Among orthometalated complexes, an iridium complex and aplatinum complex are preferable, an orthometalated iridium complex ismore preferable, and a compound having a partial structure representedby general formula K-0 (described later) is particularly preferable.

The orthometalated complex referred to herein is a generic designationof the group of compounds described in Akio Yamamoto, Yûki KinzokuKagaku, Kiso to Ôyô (“Organic Metal Chemistry, Fundamentals andApplications”, Shôkabô, 1982), pp. 150 and 232, and in H. Yersin,Photochemistry and Photophysics of Coordination Compounds (New York:Springer-Verlag, 1987), pp. 71-77 and pp. 135-146.

The light-emitting element preferably contains, as the light-emittingmaterial, the compound having the partial structure represented by thefollowing general formula K-0 (hereinafter, sometimes referred to as“iridium compound”). Among iridium compounds, a compound having aphosphorescence quantum yield and a phosphorescence emission maximumwavelength λmax that are within the ranges described above is preferred.The general formula K-0 will be described in detail below.

The light-emitting material in the present invention functions in thestate of being contained in the light-emitting layer of thelight-emitting element or in a plurality of organic compound layersincluding the light-emitting layer.

In the general formula K-0, R¹ to R⁷ each independently represents ahydrogen atom or a substituent, provided that, if R² is a fluorine atom,R³ shall not be a hydrogen atom. Examples of the substituent includegroups, which will be described later for R¹¹ in the general formulaK-0. R¹ in the general formula K-0 is preferably a hydrogen atom, analkyl group, an aryl group or a heteroaryl group, and more preferably ahydrogen atom. R² in the general formula K-0 is preferably a hydrogenatom, an alkyl group, an aryl group, a heteroaryl group or a fluorineatom, and more preferably a hydrogen atom, fluorine atom, or alkylgroup. R³ in the general formula K-0 is preferably a hydrogen atom, analkyl group, an aryl group, a heteroaryl group or a fluorine atom, morepreferably a hydrogen atom or a fluorine atom, and further preferably afluorine atom.

R⁵ in the general formula K-0 is preferably a hydrogen atom, an alkylgroup, a substituted or unsubstituted amino group or an alkoxy group,more preferably a hydrogen atom, alkyl group, or an alkoxy group, andfurther preferably a hydrogen atom. R⁴, R⁶, and R⁷ are each preferably ahydrogen atom or an alkyl group, and more preferably a hydrogen atom.

In the general formula K-0, the valence of the iridium atom in theiridium compound is not particularly limited, and is preferablytrivalent. The iridium compound may be a so-called single nucleuscomplex containing one iridium atom and may also be a so-calledmultinuclei complex containing two or more iridium atoms. Among these, asingle nucleus complex containing one iridium atom is preferred. Theiridium compound may contain a metallic atom other than iridium, and acompound containing a central metal being only an iridium atom ispreferred.

The iridium compound may have various kinds of ligands in the structurethereof. Examples of the ligand include ligands disclosed in H. Yersin,Photochemistry and Photophysics of Coordination Compounds (New York:Springer-Verlag, 1987) and in Akio Yamamoto, Yûki Kinzoku Kagaku, Kisoto Ôyô (“Organic Metal Chemistry, Fundamentals and Applications”,Shôkabô, 1982). The ligand may be either a unidentate ligand or abidentate ligand. As the ligand, a halogen ligand (preferably a chlorineligand), a nitrogen-containing heterocyclic ligand (such asphenylpyridine, benzoquinoline, quinolinole, bipyridyl andphenanthroline), a diketone ligand and a carboxylic acid ligand arepreferred, and a diketone ligand (such as acetylacetone) is morepreferred. The ligand contained in the iridium compound may be of onekind or two or more kinds. The ligand contained in the iridium compoundis preferably of one or two kinds, and particularly of one kind. Theiridium compound may be either a neutral complex having no electriccharge or an anionic complex having a counter salt (such as a chlorideion, a PF₆ ion and a ClO₄ ion). Among these, a neutral complex ispreferred.

The number of carbon atoms contained in the iridium compound ispreferably from 15 to 100, more preferably from 20 to 70, and furtherpreferably from 30 to 60.

The compound having the partial structure represented by the generalformula K-0 is preferably a compound having a partial structurerepresented by the general formula K-I, or a compound having a partialstructure represented by the general formula K-III, and more preferablya compound having a partial structure represented by the general formulaK-III. The compound having the partial structure represented by thegeneral formula K-I is preferably an iridium complex represented by thegeneral formula K-II, and more preferably an iridium complex representedby the general formula K-V. The compound having the partial structurerepresented by the general formula K-III is preferably an iridiumcomplex represented by the general formula K-IV, and more preferably aniridium complex represented by the general formula K-VI.

Next, the general formula K-I will be described.

In the general formula K-I, R¹¹ and R¹² each independently represents ahydrogen atom or a substituent. Examples of the substituent include analkyl group (preferably having from 1 to 30 carbon atoms, morepreferably having from 1 to 20 carbon atoms, and particularly preferablyhaving from 1 to 10 carbon atoms, such as methyl, ethyl, iso-propyl,tert-butyl, n-octyl, n-decyl, n-hexadecyl, cyclopropyl, cyclopentyl andcyclohexyl), an alkenyl group (preferably having from 2 to 30 carbonatoms, more preferably having from 2 to 20 carbon atoms, andparticularly preferably having from 2 to 10 carbon atoms, such as vinyl,allyl, 2-butenyl and 3-pentenyl), an alkynyl group (preferably havingfrom 2 to 30 carbon atoms, more preferably having from 2 to 20 carbonatoms, and particularly preferably having from 2 to 10 carbon atoms,such as propargyl and 3-pentynyl), an alkyl group (preferably havingfrom 6 to 30 carbon atoms, more preferably having from 6 to 20 carbonatoms, and particularly preferably having from 6 to 12 carbon atoms,such as phenyl, p-methylphenyl, naphthyl and anthranyl), an amino group(preferably having from 0 to 30 carbon atoms, more preferably havingfrom 0 to 20 carbon atoms, and particularly preferably having from 0 to10 carbon atoms, such as amino, methylamino, dimethylamino,diethylamino, dibenzylamino, diphenylamino and ditolylamino), an alkoxygroup (preferably having from 1 to 30 carbon atoms, more preferablyhaving from 1 to 20 carbon atoms, and particularly preferably havingfrom 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy and2-ethylhexyloxy), an aryloxy group (preferably having from 6 to 30carbon atoms, more preferably having from 6 to 20 carbon atoms, andparticularly preferably having from 6 to 12 carbon atoms, such asphenyloxy, 1-naphtyloxy and 2-naphthyloxy), a heteroaryloxy group(preferably having from 1 to 30 carbon atoms, more preferably havingfrom 1 to 20 carbon atoms, and particularly preferably having from 1 to12 carbon atoms, such as pyridyloxy, pyradyloxy, pyrimidyloxy andquinolyloxy), an acyl group (preferably having from 1 to 30 carbonatoms, more preferably having from 1 to 20 carbon atoms, andparticularly preferably having from 1 to 12 carbon atoms, such asacetyl, benzoyl, formyl and pivaloyl), an alkoxycarbonyl group(preferably having from 2 to 30 carbon atoms, more preferably havingfrom 2 to 20 carbon atoms, and particularly preferably having from 2 to12 carbon atoms, such as methoxycarbonyl and ethoxycarbonyl), anaryloxycarbonyl group (preferably having from 7 to 30 carbon atoms, morepreferably having from 7 to 20 carbon atoms, and particularly preferablyhaving from 7 to 12 carbon atoms, such as phenyloxycarbonyl), an acyloxygroup (preferably having from 2 to 30 carbon atoms, more preferably from2 to 20 carbon atoms, and particularly preferably having from 2 to 10carbon atoms, such as acetoxy and benzoyloxy), an acylamino group(preferably having from 2 to 30 carbon atoms, more preferably havingfrom 2 to 20 carbon atoms, and particularly preferably having from 2 to10 carbon atoms, such as acetylamino and benzoylamino), analkoxycarbonylamino group (preferably having from 2 to 30 carbon atoms,more preferably having from 2 to 20 carbon atoms, and particularlypreferably having from 2 to 12 carbon atoms, such asmethoxycarbonylamino), an aryloxycarbonylamino group (preferably havingfrom 7 to 30 carbon atoms, more preferably having from 7 to 20 carbonatoms, and particularly preferably having from 7 to 12 carbon atoms,such as phenyloxycarbonylamino), a sulfonylamino group (preferablyhaving from 1 to 30 carbon atoms, more preferably having from 1 to 20carbon atoms, and particularly preferably having from 1 to 12 carbonatoms, such as methanesulfonylamino and benzenesulfonylamino), asulfamoyl group (preferably having from 0 to 30 carbon atoms, morepreferably having from 0 to 20 carbon atoms, and particularly preferablyhaving from 0 to 12 carbon atoms, such as sulfamoyl, methylsulfamoyl,dimethylsulfamoyl and phenylsulfamoyl), a carbamoyl group (preferablyhaving from 1 to 30 carbon atoms, more preferably having from 1 to 20carbon atoms, and particularly preferably having from 1 to 12 carbonatoms, such as carbamoyl, methylcarbamoyl, diethylcarbamoyl andphenylcarbamoyl), an alkylthio group (preferably having from 1 to 30carbon atoms, more preferably having from 1 to 20 carbon atoms, andparticularly preferably having from 1 to 12 carbon atoms, such asmethylthio and ethylthio), an arylthio group (preferably having from 6to 30 carbon atoms, more preferably having from 6 to 20 carbon atoms,and particularly preferably having from 6 to 12 carbon atoms, such asphenylthio), a heteroarylthio group (preferably having from 1 to 30carbon atoms, more preferably having from 1 to 20 carbon atoms, andparticularly preferably having from 1 to 12 carbon atoms, such aspyridylthio, 2-benzimidazolylthio, 2-benzoxazolylthio and2-benzthiazolylthio), a sulfonyl group (preferably having from 1 to 30carbon atoms, more preferably having from 1 to 20 carbon atoms, andparticularly preferably having from 1 to 12 carbon atoms, such as mesyland tosyl), a sulfinyl group (preferably having from 1 to 30 carbonatoms, more preferably having from 1 to 20 carbon atoms, andparticularly preferably having from 1 to 12 carbon atoms, such asmethanesulfinyl and benzenesulfinyl), an ureido group (preferably havingfrom 1 to 30 carbon atoms, more preferably having from 1 to 20 carbonatoms, and particularly preferably having from 1 to 12 carbon atoms,such as ureido, methylureido and phenylureido), a phosphoamide group(preferably from 1 to 30 carbon atoms, more preferably from 1 to 20carbon atoms, particularly preferably from 1 to 12 carbon atoms, such asdiethylphosphoamide and phenylphosphoamide), a hydroxyl group, amercapto group, a halogen atom (such as a fluorine atom, a chlorineatom, a bromine atom and an iodine atom), a cyano group, a sulfo group,a carboxyl group, a nitro group, a hydroxamic acid group, a sulfinogroup, a hydrazino group, an imino group, a heterocyclic group (such asan aliphatic heterocyclic group and a heteroaryl group, preferablyhaving from 1 to 30 carbon atoms, and more preferably having from 1 to12 carbon atoms, examples of the hetero atom including a nitrogen atom,an oxygen atom and a sulfur atom, and examples of the heterocyclic groupincluding imidazolyl, pyridyl, quinolyl, furyl, thienyl, piperidyl,morphorino, benzoxazolyl, benzimidazolyl, benzthiazolyl and carbazolyl),and a silyl group (preferably having from 3 to 40 carbon atoms, morepreferably from 3 to 30 carbon atoms, and particularly preferably havingfrom 3 to 24 carbon atoms, such as trimethylsilyl and triphenylsilyl).These substituents may further be substituted.

R¹¹ in the general formula K-I is preferably a hydrogen atom, an alkylgroup, an aryl group or a heteroaryl group, and more preferably ahydrogen atom.

R¹² in the general formula K-I is preferably a hydrogen atom, an alkylgroup, an aryl group, a heteroaryl group or a fluorine atom, morepreferably a hydrogen atom or a fluorine atom, and further preferably afluorine atom.

R¹³, R¹⁴, R¹⁵, and R¹⁶ in the general formula K-I each independentlyrepresents a hydrogen or a substituent. Two or more of substituents maybe combined with each other to form a cyclic structure. The substituentmay be any group of R¹¹. R¹⁴ in the general formula K-I is preferably ahydrogen atom, an alkyl group, a substituted or unsubstituted aminogroup or an alkoxy group, more preferably a hydrogen atom, an alkylgroup, or an alkoxy group, and particularly preferably a hydrogen atom.

R¹³, R¹⁵ and R¹⁶ in the general formula K-I are each preferably ahydrogen atom or an alkyl group, and more preferably a hydrogen atom.

Next, the general formula K-II will be described. In the general formulaK-II, R²¹, R²², R²³, R²⁴, R²⁵, and R²⁶ each has the same meaning as R¹¹,R¹², R¹³, R¹⁴, R¹⁵, and R¹⁶ in the general formula K-I, and preferredranges thereof are also the same.

L²¹ in the general formula K-II represents a ligand. Examples of theligand include ligands disclosed in H. Yersin, Photochemistry andPhotophysics of Coordination Compounds (Springer-Verlag, 1987) and inAkio Yamamoto, Yûki Kinzoku Kagaku, Kiso to Ôyô (“Organic MetalChemistry, Fundamentals and Applications”, Shôkabô, 1982). As theligand, a halogen ligand (preferably a chlorine ligand), anitrogen-containing heterocyclic ligand (such as phenylpyridine,benzoquinoline, quinolinole, bipyridyl and phenanthroline), a diketoneligand, and a carboxylic acid ligand are preferred. Anitrogen-containing heterocyclic ligand and a diketone ligand are morepreferred.

n²¹ in the general formula K-II represents an integer of 1 to 3, andmore preferably 2 or 3. n²² in the general formula K-II represents aninteger of 0 to 4, and more preferably 0 or 1.

Next, the general formula K-III will be described. R³¹ and R³² in thegeneral formula K-III each independently represents a hydrogen atom or asubstituent. The substituent may be any group of R¹¹ in the generalformula K-I. R³¹ in the general formula K-III is preferably a hydrogenatom, an alkyl group, an aryl group, or a heteroaryl group, and morepreferably a hydrogen atom. R³² in the general formula K-III ispreferably a hydrogen atom, an alkyl group, an aryl group, a heteroarylgroup, or a fluorine atom, more preferably a hydrogen atom or a fluorineatom, and further preferably a hydrogen atom.

R³³ to R³⁶ in the general formula K-III each independently represents ahydrogen atom or a substituent. Two or more of substituents may becombined with each other to form a cyclic structure. The substituent maybe any group of R¹¹ in the general formula K-I. R³⁴ in the generalformula K-III is preferably a hydrogen atom, an alkyl group, asubstituted or unsubstituted amino group or an alkoxy group, morepreferably a hydrogen atom, an alkyl group, or an alkoxy group, andfurther preferably a hydrogen atom. R³³, R³⁵, and R³⁶ in the generalformula K-III are each preferably a hydrogen atom or an alkyl group, andmore preferably a hydrogen atom.

Next, the general formula K-IV will be described.

In the general formula K-IV, R⁴¹, R⁴², R⁴³, R⁴⁴, R⁴⁵, and R⁴⁶ each hasthe same meaning as R³¹, R³², R³³, R³⁴, R³⁵, and R³⁶ in the generalformula K-III, and preferred ranges thereof are also the same. L⁴¹ inthe general formula K-IV has the same meaning as L²¹ in the generalformula K-II, and a preferred range thereof is also the same. n⁴¹ in thegeneral formula K-IV represents an integer of 1 to 3, and preferably 1or 2. n⁴² in the general formula K-IV represents an integer of 0 to 4,and preferably 0 or 1.

Next, the general formula K-V will be described. In the general formulaK-V, R⁵³, R⁵⁴, R⁵⁵, R⁵⁶, L⁵¹, n⁵¹, and n⁵² each has the same meaning asR²³, R²⁴, R²⁵, R²⁶, L²¹, n²¹, and n²² in the general formula K-II, andpreferred ranges thereof are also the same.

Next, the general formula K-VI will be described. In the general formulaK-VI, R⁶³, R⁶⁴, R⁶⁵, R⁶⁶, L⁶¹, n⁶¹, and n⁶² each has the same meaning asR⁴³, R⁴⁴, R⁴⁵, R⁴⁶, L⁴¹, n⁴¹, and n⁴² in the general formula K-IV, andpreferred ranges thereof are also the same.

The iridium compound may be either a so-called low molecular weightcompound or a so-called oligomer compound and a so-called polymercompound containing repeating units having the partial structurerepresented by the general formula K-0 (which preferably contain aweight average molecular weight (polystyrene standard) of from 1,000 to5,000,000, more preferably from 2,000 to 1,000,000, and furtherpreferably from 3,000 to 100,000). Among these, it is preferable thatthe iridium compound is a low molecular weight compound.

Example compounds (K-1) to (K-25) of the iridium compound having thepartial structure represented by the general formula K-0 will bedescribed below, but the invention is not limited to the same.

The compound having the partial structure represented by the generalformula K-0 can be synthesized by various methods. For example, thevarious ligands or a dissociated product thereof and the iridiumcompound are reacted in the presence of a solvent (such as ahalogen-substituted hydrocarbon, an alcohol, an ether and water) or theabsence of a solvent, and in the presence of a base (such as variouskinds of inorganic and organic bases, e.g., sodium methoxide, t-butoxypotassium, triethylamine and potassium carbonate) or the absence of abase, at room temperature or under heating (in which a method of heatingby microwave is also effective as well as ordinary heating). Examples ofthe starting material include iridium (III) chloride,trisacetylacetonato iridium (III), potassium hexachloroiridate (III),potassium hexachloroiridate (IV) and an analogue thereof.

The iridium complex represented by the general formula K-II and theiridium complex represented by the general formula K-IV can be utilizedas a material for a light-emitting element and can also be used formedical uses, fluorescent whitening agents, photographic materials, UVabsorbing materials, laser dyes, dyes for color filters and colorconversion filters.

In another embodiment of the light-emitting element of the presentinvention, the light-emitting element comprises a light-emitting layer,or a plurality of organic compound layers including the light-emittinglayer disposed between a pair of electrodes comprising an anode and acathode, with at least one layer of the organic compound layersincluding at least one kind of the iridium compound. Since the iridiumcompound has the characteristic of emitting blue light at highefficiency, the light emission efficiency of the light-emitting elementcan be improved by containing the compound in the light-emitting layer.Moreover, since the iridium compound has excellent charge transportingcapability, the light emission efficiency of the light-emitting elementcan also be improved by containing the compound in the chargetransporting layer. As a result, a light-emitting element can beprovided that reduces energy consumption at the time of light emissionand that can emit blue light at a high luminance for a long period oftime.

The light-emitting element may further comprise, in addition to thelight-emitting layer between the electrodes, a hole implantation layer,a hole transporting layer, an electron implantation layer, an electrontransporting layer and a protective layer. These layers may each haveother functions. In the light-emitting element, it is preferable todispose between the cathode and the light-emitting layer a layercontaining a compound having an ionization potential of 5.9 eV or more,and more preferably from 6.0 to 7.0 eV. It is more preferable to disposean electron transporting layer having an ionization potential of 5.9 eVor more. Various kinds of materials can be used to form the layers. Inthe light-emitting element, the iridium compound may be contained, asthe light-emitting material, in the light-emitting layer and also in thecharge transporting layer.

The method for forming the layer containing the iridium compound is notparticularly limited, and various methods, such as a vacuum depositionmethod, an LB method, a resistance heating vapor deposition method, anelectron beam method, a sputtering method, a molecular accumulationmethod, a coating method (such as a spin coating method, a castingmethod and a dip coating method), an ink jet method and a printingmethod, can be utilized. A resistance heating vapor deposition methodand a coating method are preferred from the standpoint ofcharacteristics and production. In particular, the coating method isadvantageous in that production cost can be reduced when thelight-emitting element is applied to a technology that requires a largearea, such as a display.

The layer can be formed by the coating method in the following manner.The iridium compound is dissolved in a solvent to prepare a coatingcomposition, which is then coated on a desired layer (or electrode),followed by drying. The coating composition may contain a resin, and theresin may be in a dissolved state in the solvent or in a dispersed statetherein. Examples of the resin include a non-conjugated system polymer(such as polyvinyl carbazole) and a conjugated system polymer (such as apolyolefin series polymer). Specific examples thereof include polyvinylchloride, polycarbonate, polystyrene, polymetyl methacrylate, polybutylmethacrylate, polyester, polysulfone, polyphenylene oxide,polybutadiene, poly(N-vinylcarbazole), hydrocarbon resin, ketone resin,phenoxy resin, polyamide, ethylcellulose, vinyl acetate, ABS resin,polyurethane, melamine resin, unsaturated polyester resin, alkyd resin,epoxy resin and silicone resin.

The anode is to supply holes to the hole implantation layer, the holetransporting layer and the light-emitting layer, and may comprise ametal, an alloy, a metallic oxide, an electroconductive compound or amixture thereof, and preferably a material having a work function of 4eV or more. Specific examples thereof include electroconductive metallicoxides, such as tin oxide, zinc oxide, indium oxide and indium tin oxide(ITO), metals, such as gold, silver, chromium and nickel, mixtures oraccumulated products of metal and electroconductive metallic oxide,inorganic electroconductive substances, such as copper iodide and coppersulfide, organic electroconductive materials, such as polyaniline,polythiophen and polypyrrole, and accumulated products of these and ITO.Among these, electroconductive metallic oxide is preferable, and ITO isparticularly preferable from the standpoint of productivity, highelectroconductivity and transparency. The film thickness of the anodecan be appropriately selected depending on the material, and ispreferably from 10 nm to 5 μm, more preferably from 50 nm to 1 μm, andfurther preferably from 100 to 500 nm.

The anode is generally formed as a layer on a transparent substrate,such as soda lime glass, non-alkali glass or a transparent resinsubstrate. When glass is used as the transparent substrate, the glassmaterial is preferably non-alkali glass in order to reduce eluting ionsfrom the glass. When soda lime glass is used, it is preferable to use asoda lime glass having a barrier coating of, for example, silica. Thethickness of the substrate is not particularly limited as long as itsufficiently maintains mechanical strength, and is generally 0.2 mm ormore, and preferably 0.7 mm or more when glass is used.

The anode can be produced by various methods depending on the material,and in the case of ITO, the film thereof may be produced by an electronbeam method, a sputtering method, a resistance heating vapor depositionmethod, a chemical reaction method (a sol-gel method) and coating of anindium tin oxide dispersion. When the anode is subjected to varioustreatments, such as cleaning, the driving voltage of the light-emittingelement can be decreased, and light emission efficiency thereof can beimproved. In the case of ITO, for example, a UV-ozone treatment and aplasma treatment are effective.

The cathode is to supply electrons to the electron implantation layer,the electron transporting layer and the light-emitting layer, and isselected in consideration of adhesion to the layer adjacent to thecathode, such as the electron implantation layer, the electrontransporting layer and the light-emitting layer, ionization potentialand stability. Examples of the material of the cathode include metals,alloys, metallic halogenides, metallic oxides, electroconductivecompounds and mixtures thereof. Specific examples thereof include alkalimetals (such as Li, Na and K) and fluorides or oxides thereof, alkalineearth metals (such as Mg and Ca) and fluorides or oxides thereof, gold,silver, lead, alloys or metallic mixtures of sodium and potassium,alloys or metallic mixtures of lithium and aluminum, alloys or metallicmixtures of magnesium and silver, and rare earth metals, such as indiumand ytterbium. Among these, a material having a work function of 4 eV orless is preferable, and aluminum, an alloy or a metallic mixture oflithium and aluminum and an alloy of a metallic mixture of magnesium andsilver are more preferable. The cathode may have a single layerstructure of the compounds and the mixture, or an accumulated layerstructure containing the compounds and the mixtures. For example,accumulated layer structures of aluminum/lithium fluoride andaluminum/lithium oxide are preferable. The film thickness of the cathodecan be appropriately selected depending on the material, and ispreferably from 10 nm to 5 μm, more preferably from 50 nm to 1 μm, andfurther preferably from 100 nm to 1 μm.

The cathode can be produced by various methods, such as an electron beammethod, a sputtering method, a resistance heating vapor depositionmethod and a coating method, and a single component of a metal may bevapor-deposited or, alternatively, two or more components may besimultaneously vapor-deposited. Furthermore, plural metals may besimultaneously vapor-deposited to form an alloy electrode, and an alloyhaving been prepared may be vapor-deposited.

The sheet resistance of the anode and the cathode is preferably as lowas possible, and is preferably several hundreds Ω per square or less.

The material of the light-emitting layer is not particularly limited aslong as it is capable of forming a layer in which it is possible forholes to be implanted thereto from the anode, the hole implantationlayer or the hole transporting layer upon application of an electricfield, and in which it is possible for electrons to be implanted theretofrom the cathode, an electron implantation layer or the electrontransporting layer. The material of the light-emitting layer must alsofunction to move the implanted charge and to provide a place for therecombination of holes and electrons to emit light. The light-emittinglayer preferably contains the iridium compound as the light-emittingmaterial since it enables blue light emission with high efficiency.However, when the iridium compound is contained in the organic compoundlayers other than the light-emitting layer, other light-emittingmaterials may be used. Examples of other light-emitting materialsinclude various kinds of metallic complexes and rare earth complexes ofa benzoxazole derivative, a benzimidazole derivative, a benzthiazolederivative, a styrylbenzene derivative, a polyphenyl derivative, adiphenylbutadiene derivative, a tetraphenylbutadiene derivative, anaphthalimide derivative, a coumarin derivative, a perylene derivative,a perynone derivative, an oxadiazole derivative, an aldadine derivative,a pyraridine derivative, a cyclopentadiene derivative, abisstyrylanthracene derivative, a quinacridone derivative, apyrrolopyridine derivative, a thiadiazolopyridine derivative, acyclopentadiene derivative, a styrylamine derivative, an aromaticdimethylidyne derivative, and an 8-quinolinole derivative, a polymercompound, such as polythiophene, polyphenylene andpolyphenylenevinylene, and an organic silane compound. In thelight-emitting layer, any of the other light-emitting compounds may beused in combination with the iridium compound.

A host material with the iridium compound as a guest material may becontained in the light-emitting layer along with the iridium compound.Examples of the host material include one having a carbazole skeleton,one having a diarylamine skeleton, one having a pyridine skeleton, onehaving a pyrazine skeleton, one having a triazine skeleton and onehaving an arylsilane skeleton. The host material preferably has theenergy level of the minimum triplet excited state, T₁, which is greaterthan the level of T₁ of the guest material. The host material may beeither a low molecular weight compound or a high molecular weightcompound. The host material and the light-emitting material, such as theiridium compound, are subjected to simultaneous vapor deposition to formthe light-emitting layer comprising the host material doped with thelight-emitting material.

The film thickness of the light-emitting layer is not particularlylimited, and in general, it is preferably from 1 nm to 5 μm, morepreferably from 5 nm to 1 μm, and further preferably from 10 nm to 500nm.

The method for forming the light-emitting layer is not particularlylimited, and a resistance heating vapor deposition method, an electronbeam method, a sputtering method, a molecular accumulation method, acoating method (such as a spin coating method, a casting method and adip coating method), an inkjet method, a printing method and an LBmethod may be used with a resistance heating vapor deposition method andthe coating method being preferred.

The material for the hole implantation layer and the hole transportinglayer may be a material having one of a function to implant holes fromthe anode, a function to transport the holes, and a function to obstructelectrons implanted from the cathode. Specific examples thereof includea carbazole derivative, a triazole derivative, an oxazole derivative, anoxadiazole derivative, an imidazole derivative, a polyarylalkanederivative, a pyrazoline derivative, a pyrazolone derivative, aphenylenediamine derivative, an arylamine derivative, anamino-substituted chalcone derivative, a styrylanthracene derivative, afluorenone derivative, a hydrazone derivative, a stilbene derivative, asilazane derivative, an aromatic tertiary amine compound, a styrylaminecompound, an aromatic dimethylidyne series compound, a porphyrin seriescompound, an oligomer of an electroconductive polymer, such as apolysilane series compound, a poly(N-vinylcarbazole) derivative, ananiline series copolymer, a thiophene oligomer and polythiophene, anorganic silane derivative, and the above-described iridium compound. Thefilm thickness of the hole implantation layer and the hole transportinglayer is not particularly limited, and in general, it is preferably from1 nm to 5 μm, more preferably from 5 nm to 1 μm, and further preferablyfrom 10 to 500 nm. The hole implantation layer and the hole transportinglayer may have a single layer structure of one kind or two or more kindsof materials or, alternatively, a multilayer structure comprising plurallayers having the same composition or different compositions. The sameforming methods as those listed for the formation of the layercontaining the iridium compound can be applied to the formation of thehole implantation layer and the hole transporting layer.

The material for the electron implantation layer and the electrontransporting layer may be a material having one of a function to implantelectrons from the cathode, a function to transport the electrons, and afunction to obstruct holes implanted from the anode. Specific examplesthereof include a triazole derivative, an oxazole derivative, anoxadiazole derivative, an imidazole derivative, a fluorenone derivative,an anthraquinodimethane derivative, an anthrone derivative, adiphenylquinone derivative, a thiopyran dioxide derivative, acarbodiimide derivative, a fluorenylidenemethane derivative, adistyrylpyrazine derivative, a tetracarboxylic acid anhydride of anaromatic ring, such as naphthalene and perylene, a phthalocyaninederivative, and various metallic complexes, such as a metallic complexof an 8-quinolinol derivative and a metallic complex having metalphthalocyanine, benzoxazole or benzotiazole as a ligand, an organicsilane derivative, and the iridium compound. The film thickness of theelectron implantation layer and the electron transporting layer is notparticularly limited, and in general, it is preferably from 1 nm to 5μm, more preferably from 5 nm to 1 μm, and further preferably from 10 to500 nm. The electron implantation layer and the electron transportinglayer may have a single layer structure of one kind or two or more kindsof the materials or, alternatively, a multilayer structure comprisingplural layers having the same composition or different compositions. Thesame forming methods as those listed for forming the layer containingthe iridium compound can be applied to the formation of the electronimplantation layer and the electron transporting layer.

The material for the protective layer may be those having a function tosuppress entrance of substances that accelerate deterioration of theelement, such as moisture and oxygen, into the element. Specificexamples thereof include metals, such as In, Sn, Pb, Au, Cu, Ag, Al, Tiand Ni, metallic oxides, such as MgO, SiO, SO₂, Al₂O₃, GeO, NiO, CaO,BaO, Fe₂O₃, Y₂O₃ and TiO₂, metallic nitrides, such as SiN_(x) andSiN_(x)O_(y), metallic fluorides, such as MgF₂, LiF, AlF₃ and CaF₂,polyethylene, polypropylene, polymethyl methacrylate, polyimide,polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene,polydichlorodifluoroethylene, a copolymer of chlorotrifluoroethylene anddichlorodifluoroethylene, a copolymer obtained by copolymerizing amonomer mixture containing tetrafluoroethylene and at least one kind ofa comonomer, a fluorine-containing copolymer having a cyclic structurein a copolymer main chain, a water absorbing substance having a waterabsorption of 1% or more, and a moisture preventing substance having awater absorption of 0.1% or less. The method for forming the protectivelayer is also not particularly limited, and those listed for methods ofproducing the layer containing the iridium compound can be utilized.

The light-emitting element of the present invention can be applied totechnologies in various fields, such as display devices, displays,backlights, electrophotography, illumination light sources, recordinglight sources, exposure light sources, read light sources, signs,signboards and interior, optical communication.

The present invention will be further described in detail with referenceto the following examples, but the present invention should not beconstrued as being limited to the same.

SYNTHESIS EXAMPLE 1 Synthesis of Example Compound K-1

1.77 g of 2-(4-fluorophenyl)pyridine, 0.5 g of trisacetylacetonatoiridium (III) and 30 ml of glycerol were mixed and then stirred under anitrogen stream at 200° C. for 4 hours. After cooling to roomtemperature, 200 ml of methanol was added thereto, and a solid matterthus deposited was filtered out. The solid matter was purified withsilica gel column chromatography (eluent: chloroform) to obtain 0.5 g ofa pale yellow solid matter. The NMR measurement thereof revealed thatthe resulting compound was the example compound K-1.

The phosphorescence quantum yield of the resulting example compound K-1was measured after degassing oxygen (solvent: toluene, concentration:5.0×10⁻⁶ mol/L), and it was 90%. The phosphorescence emission maximumwavelength λmax was 477 nm.

SYNTHESIS EXAMPLE 2 Synthesis of Example Compound K-3

3.0 g of 2-(2,4-difluorophenyl)pyridine, 1.3 g of trisacetylacetonatoiridium (III) and 50 ml of glycerol were mixed and then stirred under anitrogen stream at 200° C. for 4 hours. After cooling to roomtemperature, 200 ml of methanol was added thereto, and a solid matterthus deposited was filtered out. The solid matter was purified withsilica gel column chromatography (eluent: chloroform) to obtain 0.8 g ofa pale yellow solid matter. The NMR measurement thereof revealed thatthe resulting compound was the example compound K-3.

The phosphorescence quantum yield of the resulting example compound K-3was measured after degassing oxygen (solvent: toluene, concentration:5.0×10⁻⁶ mol/L), and it was 70%. The phosphorescence emission maximumwavelength λmax was 470 nm.

SYNTHESIS EXAMPLE 3 Synthesis of Example Compound K-9

10 ml of chloroform was added to 0.2 g of compound (a) and 0.07 ml ofacetylacetone, and 0.13 ml of methanol solution of sodium methoxide (28%by weight) was further added thereto and then stirred under a reflux for6 hours. After cooling to room temperature, 50 ml of chloroform and 50ml of water were added thereto, and an organic layer was separated. Theorganic layer was purified with silica gel column chromatography(eluent: chloroform) to obtain 0.1 g of a pale yellow solid matter. TheNMR measurement thereof revealed that the resulting compound was theexample compound K-9.

SYNTHESIS EXAMPLE 4 Synthesis of Example Compound K-11

1.0 g of 2-(2,4-difluorophenyl)-4-methylpyridine, 1.0 g oftrisacetylacetonato iridium (III) and 30 ml of glycerol were mixed andthen stirred under a nitrogen stream at 200° C. for 4 hours. Aftercooling to room temperature, 200 ml of water was added thereto, and asolid matter thus deposited was filtered out. The solid matter waspurified with silica gel column chromatography (eluent: chloroform) toobtain 0.2 g of a pale yellow solid matter. The NMR measurement thereofrevealed that the resulting compound was the example compound K-11.

COMPARATIVE EXAMPLE 1

A cleaned ITO substrate was installed in a vapor deposition apparatus,on which α-NPD (N,N′-diphenyl-N,N′-di(α-naphthyl)benzidine wasvapor-deposited to a thickness of 40 nm, the compound A and the compoundB (disclosed in Applied Physics Letters, Vol. 75, No. 1 (5 Jul. 1999))shown below were vapor-deposited (weight ratio: 10/1) to a thickness of24 nm, and the compound E shown below was further vapor-depositedthereon to a thickness of 24 nm, so as to form an organic thin film.After providing a patterned mask (providing a light emission area of 4mm×5 mm) on the organic thin film, magnesium and silver (10/1) weresimultaneously vapor-deposited to a thickness of 50 nm, and then silverwas vapor-deposited to a thickness of 50 nm, whereby an organic ELdevice was produced.

The phosphorescence quantum yield of the compound B was measured in thesame manner as the example compound K-1, and it was 70%. Thephosphorescence emission maximum wavelength λmax was 507 mm.

The resulting organic EL device was subjected to light emission byapplying a constant direct current voltage by using a source measuringunit, Type 2400 produced by Toyo Corp., and the brightness and the lightemission wavelength were measured by using a luminance meter, BM-8produced by Topcon Corp., and a spectrum analyzer, PMA-11 produced byHamamatsu Photonics Co., Ltd., respectively. As a result, green lightemission of a light emission wavelength λmax of 516 nm and a CIEchromaticity value (x, y) of (0.29, 0.62) was obtained, and the externalquantum efficiency thereof was 13.6%.

COMPARATIVE EXAMPLE 2

An organic EL device was produced in the same manner as in ComparativeExample 1 except that the compound C (disclosed in Polymer Preprints,Vol. 41(1), p. 770 (2000)) shown below was used instead of the compoundB and then evaluated in the same manner. As a result, green lightemission of a light emission wavelength λmax of 505 nm and a CIEchromaticity value (x, y) of (0.27, 0.57) was obtained, and the externalquantum efficiency thereof was 3.3%.

Compound C (described in Polymer Preprints, Vol. 41(1), p. 770 (2000))

It was understood from the results of Comparative Examples 1 and 2 thatonly green light emission could be obtained by the organic EL devicescontaining the known orthometalated iridium complexes.

COMPARATIVE EXAMPLE 3

A cleaned ITO substrate was installed in a vapor deposition apparatus,on which α-NPD (N,N′-diphenyl-N,N′-di(α-naphthyl)benzidine) wasvapor-deposited to a thickness of 40 nm, and the following compound F(DPVBi) was vapor-deposited thereon to a thickness of 20 nm. Thecompound E was further vapor-deposited thereon to a thickness of 40 nm,and the cathode was vapor-deposited in the same manner as in ComparativeExample 1, so as to produce an organic EL device.

The resulting organic EL device was subjected to light emission byapplying a constant direct current voltage in the same manner as inComparative Example 1. As a result, blue light emission of a CIEchromaticity value (x, y) of (0.15, 0.20) was obtained, but the externalquantum efficiency thereof was as low as 1.2%. It was understood fromthe results of Comparative Example 3 that the known blue light-emittingelement had a low external quantum efficiency, which was far lower than5%.

EXAMPLE 1

An organic EL device was produced in the same manner as in ComparativeExample 1 except that the example compound K-I was used instead of thecompound B and then evaluated in the same manner. As a result, bluelight emission of a light emission wavelength λmax of 486 nm and a CIEchromaticity value (x, y) of (0. 18, 0.49) was obtained, and theexternal quantum efficiency thereof was 5.8%.

EXAMPLE 2

An organic EL device was produced in the same manner as in ComparativeExample 1 except that the example compound K-1 was used instead of thecompound B, the compound D shown below was used instead of the compoundA, and then evaluated in the same manner. As a result, blue lightemission of a light emission wavelength λmax of 487 nm and a CIEchromaticity value (x, y) of (0.22, 0.53) was obtained, and the externalquantum efficiency thereof was 10.5%.

EXAMPLE 3

A cleaned ITO substrate was installed in a vapor deposition apparatus,on which TPD (N,N′-diphenyl-N,N′-di(m-tolyl)benzidine wasvapor-deposited to a thickness of 50 nm, the compound K-1 and thecompound D were vapor-deposited (weight ratio: 1/17) to a thickness of36 nm, and the compound G was further vapor-deposited thereon to athickness of 36 nm, so as to form an organic thin film. After providinga patterned mask (providing a light emission area of 4 mm×5 mm) on theorganic thin film, lithium fluoride was vapor-deposited in the vapordeposition apparatus to a thickness of 3 nm, and then aluminum wasvapor-deposited to a thickness of 40 nm, whereby an organic EL devicewas produced. As a result, blue light emission of a light emissionmaximum wavelength λmax of 485 nm and a CIE chromaticity value (x, y) of(0.19, 0.51) was obtained, and the external quantum efficiency thereofwas 19.1%.

EXAMPLE 4

An organic EL device was produced in the same manner as in Example 3except that the example compound K-3 was used instead of the examplecompound K-1 and then evaluated in the same manner. As a result, bluelight emission of a light emission maximum wavelength λmax of 473 nm anda CIE chromaticity value (x, y) of (0.15, 0.37) was obtained, and theexternal quantum efficiency thereof was 12.9%.

EXAMPLE 5

An organic EL device was produced in the same manner as in Example 3except that the example compound K-9 was used instead of the examplecompound K-1 and then evaluated in the same manner. As a result, bluelight emission of a light emission maximum wavelength λmax of 480 nm anda CIE chromaticity value (x, y) of (0.20, 0.52) was obtained, and theexternal quantum efficiency thereof was 11.4%.

A blue light-emitting EL element of high efficiency can be produced byproducing and evaluating EL elements containing the compounds of thepresent invention in the similar manner. Blue light-emitting elements ofa coating type containing a non-conjugated system polymer (such aspolyvinyl carbazole) and a conjugated system polymer (such as apolyolefin series polymer) can also be produced.

As described in the foregoing, the light-emitting element according tothe present invention can emit blue light at high efficiency incomparison to conventional blue light-emitting elements. When thelight-emitting element of the present invention is used as a displayelement, electric power consumption can be greatly reduced, and a largearea display and long term use can be realized. A white light-emittingelement of high efficiency can be produced by a combination of alight-emitting material of red to orange colors and a light-emittingelement of red to orange colors on the basis of the blue light-emittingelement of the present invention. Furthermore, according to the presentinvention, an iridium complex that emits blue light at high efficiencycan be provided.

1. A light-emitting element comprising a pair of electrodes and alight-emitting layer, or a plurality of organic compound layerscontaining a light-emitting layer between the pair of electrodes,wherein the light-emitting layer, or the plurality of organic compoundlayers containing a light-emitting layer, comprises at least one kind ofcompound having a partial structure represented by the following generalformula K-III:

wherein R³¹ and R³³ to R³⁶ each independently represents hydrogen or asubstituent; R³² represents hydrogen; and two or more of R³³ to R³⁶ maybe combined with one another to form a cyclic structure; wherein thelight-emitting element has a light emission maximum wavelength of420-480 nm; wherein the at least one kind of compound having the partialstructure represented by general formula K-III is of the followinggeneral formula K-IV:

wherein R⁴¹ and R⁴³ to R⁴⁶ each independently represents hydrogen or asubstituent; R⁴² represents hydrogen; L⁴¹ represents a ligand; n⁴¹represents an integer of 1 to 3; and n⁴² represents an integer of 0 to4; wherein the light-emitting layer comprises at least one host materialhaving a unit which is selected from the group consisting of a pyridineunit, a pyrazine unit, a triazine unit, and an arylsilane unit.
 2. Thelight-emitting element of claim 1, wherein R⁴¹ is hydrogen, an alkylgroup, an aryl group, or a heteroaryl group.
 3. The light-emittingelement of claim 1, wherein R⁴⁴ is hydrogen, an alkyl group, asubstituted or unsubstituted amino group, or an alkoxy group.
 4. Thelight-emitting element of claim 1, wherein R⁴³, R⁴⁵ and R⁴⁶ eachindependently represents hydrogen or an alkyl group.
 5. Thelight-emitting element of claim 1, wherein n⁴¹ is 3 and n⁴² is
 0. 6. Thelight-emitting element of claim 1, wherein L⁴¹ is at least one ligandselected from the group consisting of a halogen ligand, anitrogen-containing heterocyclic ligand, a diketone ligand and acarboxylic acid ligand.
 7. The light-emitting element of claim 1,further comprising at least one layer which is selected from the groupconsisting of a hole implantation layer, a hole-transporting layer, anelectron-implantation layer, an electron-transporting layer and aprotective layer.
 8. The light-emittingelement of claim 1, wherein the yvalue of the CIE chromaticity of light emission of the light-emittingelement is 0.40 or less.
 9. A light-emitting element comprising a pairof electrodes and a light-emitting layer, or a plurality of organiccompound layers containing a light-emitting layer between the pair ofelectrodes, wherein the light-emitting layer, or the plurality oforganic compound layers containing a light-emitting layer, comprises atleast one kind of compound having a partial structure represented by thefollowing general formula K-III: General Formula K-III

wherein R³¹ and R³³ to R³⁶ each independently represents hydrogen or asubstituent; R³² represents hydrogen; and two or more of R³³ to R³⁶ maybe combined with one another to form a cyclic structure; wherein the yvalue of the CIE chromaticity of light emission of the light-emittingelement is 0.40 or less; wherein the at least one kind of compoundhaving the partial structure represented by general formula K-III is ofthe following general formula K-IV:

wherein R⁴¹ and R⁴³ to R⁴⁶ each independently represents hydrogen or asubstituent: R⁴² represents hydrogen; L⁴¹ represents a ligand; n⁴¹represents an integer of 1 to 3; and n⁴² represents an integer of 0 to4; wherein the light-emitting layer comprises at least one host materialhaving a unit which is selected from the group consisting of a pyridineunit, a pyrazine unit, a triazine unit, and an arylsilane unit.
 10. Thelight-emitting element of claim 9, wherein R⁴¹ is hydrogen, an alkylgroup, an aryl group, or a heteroaryl group.
 11. The light-emittingelement of claim 9, wherein R⁴⁴ is hydrogen, an alkyl group, asubstituted or unsubstituted amino group, or an alkoxy group.
 12. Thelight-emitting element of claim 9, wherein R⁴³, R⁴⁵ and R⁴⁶ eachindependently represents hydrogen or an alkyl group.
 13. Thelight-emitting element of claim 9, wherein n⁴¹ is 3 and n⁴² is
 0. 14.The light-emitting element of claim 9, wherein L⁴¹ is at least oneligand selected from the group consisting of a halogen ligand, anitrogen-containing heterocyclic ligand, a diketone ligand and acarboxylic acid ligand.
 15. The light-emitting element of claim 9,further comprising at least one layer which is selected from the groupconsisting of a hole-implantation layer, a hole-transporting layer, anelectron-implantation layer, an electron-transporting layer and aprotective layer.